The current disclosure is related to power machines. More particularly, the current disclosure is related to drive systems for power machines. Many power machines such as excavators, wheel loaders including skid steer loaders and steerable axle loaders, tracked loaders and the like incorporate hydraulic or hydrostatic drive systems to propel the power machine over a support surface. One component in many of these types of machines is a drive motor, which receives power in the form of pressurized hydraulic fluid from a power source and converts the power into rotational motion to drive one or more wheels, tracks or other similar devices to cause the power machine to move over the support surface. For a given pressure and flow rate, motors with a relatively high displacement deliver higher torque but at a lower speed than motors with relatively lower displacement.
In certain situations, power machines that employ a higher displacement motor are more advantageous than similar power machines that have a lower displacement motor. For example, when a power machine is engaging ground such as in a digging or grading application, ascending an incline, or negotiating a turn, a higher torque motor is more advantageous than a lower torque motor. Conversely, a high-speed motor is more advantageous in some situations. For example, when an operator wishes to move the power machine from one location to another on a generally flat surface, a lower torque motor that achieves higher travel speed is more advantageous.
Some hydraulic motors have the capability to shift from a high displacement arrangement to a low displacement arrangement in response to an operator input. However, there may be instances when an operator selects the low displacement arrangement but then operates the power machine in a way that causes a high load condition on the power machine. In such situations, a hydraulic motor on the power machine may be overloaded and stall, causing the operator to shift from a low displacement arrangement to a high displacement arrangement. Alternatively, an operator may reduce travel inputs to reduce the travel signals provided to a hydraulic pump and avoid a stalling condition, but even an experienced operator will find it extremely difficult, if not impossible, to maximize the effort of such a power machine and avoid a stalling condition.
The discussion above is merely provided for general background information and is not intended to be used as an aid in determining the scope of the claimed subject matter.